Method for manufacturing duplex stainless steel sheet having high nitrogen content and good surface quality

1. A method of manufacturing a duplex stainless steel sheet having an increased nitrogen content and an improved surface quality through a twin roll strip casting process by supplying a molten steel between two casting rolls rotating in opposite directions, the method comprising:

preparing a molten steel comprising, by wt %, carbon (C): 0.02% to 0.06%, chromium (Cr): 19.0% to 21.0%, manganese (Mn): 2.8% to 3.2%, silicon (Si): 0.55% to 0.8%, nickel (Ni): 0.5% to 1.5%, nitrogen (N): more than 2500 ppm, and a balance of iron (Fe) and inevitable impurities;

measuring a nitrogen content of the prepared molten steel;

increasing a temperature of the prepared molten steel in proportion to the measured nitrogen content to form a temperature-increased molten steel; and

supplying the temperature-increased molten steel to between two casting rolls rotating in opposite directions to form a duplex stainless steel sheet having an increased nitrogen content.

2. The method of claim 1 , wherein when the nitrogen content of the prepared molten steel is more than 2500 ppm to 3000 ppm or less, and the temperature of the temperature-increased molten steel is 1520° C. or higher.

3. The method of claim 2 , wherein the increasing comprises: increasing the temperature of the prepared molten steel by 2° C. or more each time the measured nitrogen content is increased by 10 ppm.

4. The method of claim 3 , wherein the temperature of the temperature-increased molten steel is 1520° C. to 1540° C.

5. The method of claim 1 , wherein the increasing comprises: increasing the temperature of the prepared molten steel by 2° C. or more each time the measured nitrogen content is increased by 10 ppm.

6. The method of claim 5 , wherein the temperature of the temperature-increased molten steel is 1520° C. to 1540° C.